This invention relates to a method for manufacturing a fibre optic male contact comprising a tubular body made of plastic material, a cable adaptor having a first end portion fastened into a rear end portion of said body and a second end portion extending out of said rear end portion of the body, an elongated floating ferrule extending through a front end portion of said body to house an end portion of a fibre optic core, said ferrule assembled to a tubular ferrule holder movably housed in said body and having abutment means adapted to rest against shoulder means arranged in said body between the front and rear end portions thereof, and a coil spring biased between said first end portion of the cable adaptor and said abutment means of the ferrule holder to urge the abutment means of the ferrule holder against the shoulder means of the body.
Such fibre optic male contacts are commonly used for optically coupling optic fibres to each other, or to light sources or detectors for high speed communication and data transmission. They are of particular interest where a great number of fibres have to be installed in a single connector or insert because they avoid the difficulties of individually positioning and gluing the fibres in the connector, a major drawback being that the rupture of one single fibre requires the replacement of the whole assembly. The issue is, however, to miniaturise them as much as possible to achieve an acceptable compromise between the number of fibres installed in the connector and the size of the connector or insert.
In these fibre optic male contacts, the cable adaptor is necessary to support a sheath of strain relief material such as for example Kevlar (Trade Mark) surrounded by a plastic jacket crimped on the second end portion of the cable adaptor to reinforce the fibre optic core which extends from the floating ferrule through the tubular body and cable adaptor.
Currently, the tubular body has been made of metal or plastic material with its rear end portion machined so as to form an inner thread in which the threaded first end portion of the cable adaptor was screwed after insertion of the ferrule holder and spring into the rear end portion of the tubular body. This threading technique is expensive and, most of all, it is strongly limiting the possibilities of miniaturisation of the fibre optic male contact because of the need to have a tubular body with relatively thick walls to allow machining of a sufficiently resistant thread for assembly with the cable adaptor and the need to machine longitudinal grooves in the rear end portion of the tubular body to allow guiding and passage of the abutment means of the ferrule holder therethrough up to their reaching the shoulder means of the tubular body.
An improvement has been achieved by molding the tubular body with bayonet grooves formed in its rear end portion to allow a push and twist assembly with the correspondingly studded first end portion of the cable adaptor after insertion of the ferrule holder and spring into the rear end portion of the tubular body. This results in a less expensive manufacture but there is still the problem of miniaturisation because of the need to have sufficient wall thickness for the bayonet grooving in the rear end portion of the tubular body and the need to mold in the rear end portion of the tubular body longitudinal grooves to allow guiding and passage of the abutment means of the ferrule holder therethrough up to their reaching the shoulder means of the tubular body.
It is an object of this invention to avoid these drawbacks by means of a method for manufacturing a fibre optic male connector which is versatile and cost efficient while allowing a satisfactory miniaturisation.
According to a first aspect of the invention, there is provided a method for manufacturing a fibre optic male contact comprising a tubular body made of plastic material, a cable adaptor having a first end portion fastened into a rear end portion of said body and a second end portion extending out of said rear end portion of the body, an elongated floating ferrule extending through a front end portion of said body to house an end portion of a fibre optic core, said ferrule assembled to a tubular ferrule holder movably housed in said body and having abutment means adapted to rest against shoulder means arranged in said body between the front and rear end portions thereof, and a coil spring biased between said first end portion of the cable adaptor and said abutment means of the ferrule holder to urge the abutment means of the ferrule holder against the shoulder means of the body, characterized by the steps of molding said rear end portion of the tubular body on said first end portion of the cable adaptor, inserting said coil spring and ferrule holder through said front end portion of said tubular body, momentarily at least partly expanding radially said front end portion and shoulder means of the tubular body by forcible passage of the abutment means of said ferrule holder therethrough, urging said coil spring between said first end portion of the cable adaptor and said abutment means of the ferrule holder, allowing said front end portion and shoulder means of the body to radially re-contract after passage of said abutment means, allowing said abutment means to catch said shoulder means, and releasing said ferrule holder whereby the abutment means thereof may rest against said shoulder means under the bias of the coil spring.
Accordingly, by molding the rear end portion of the tubular body on the first end portion of the cable adaptor, a sturdy assembly is achieved between the first end portion of the cable adaptor and the rear end portion of the tubular body with a minimal wall thickness of the tubular body at that level. The first end portion of the cable adaptor is mechanically anchored in the rear end portion of the tubular body, thereby assuring safest assembly at that level. There are no material weakening and space consuming threads or bayonet groovings to assemble the cable adaptor, and there are no longitudinal grooves for passage and guiding of the abutment means of the ferrule holder through the rear end portion of the tubular body. Furthermore, by taking advantage of the intrinsic elasticity of the plastic material forming the tubular body to insert the coil spring and ferrule holder through the front end portion of the tubular body and momentarily expand the front end portion and shoulder means of the tubular body radially by forcing the abutment means of the ferrule holder therethrough, there is no need to have longitudinal space consuming grooves to allow guiding and passage of the abutment means of the ferrule holder therethrough. And by further taking advantage of the intrinsic elasticity of the plastic material forming the tubular body to allow the front end portion of the tubular body and shoulder means to radially re-contract after passage of the abutment means, it suffices then to release the ferrule holder to have its abutment means resting against the shoulder means of the tubular body under the bias of the spring, thereby completing the assembly. The manufacture is cost saving and easy, and most of all an extreme miniaturisation may be achieved.
Preferably, said rear end portion of said tubular body is molded on an indentated surface of the first end portion of the cable adaptor to achieve best assembly with a minimal thickness of the material forming the tubular body.
The shoulder means may be formed by end walls of windows molded in the tubular body with said abutment means being formed by radial protrusions of the ferrule holder respectively adapted to be housed in said windows. Preferably, two diametrically opposed windows are molded in the tubular body. Forming and function of the shoulder means is thus easy and safe while assuring easy insertion of the ferrule holder and abutment means thereof through the front end portion of the tubular body and momentary expansion thereof. The window and radial protrusion arrangement further assures anti-rotation of the ferrule holder in the tubular body and proper angular positioning of the fibre optic core therein. Furthermore, the windows increase elasticity of the tubular body, thereby facilitating expansion thereof for easy forcible passage of the radial protrusions of the ferrule holder therethrough.
In a preferred configuration, said front end portion of the tubular body comprises a plurality of longitudinal slots molded therein at equal angular distance from one another. And said front end portion of the tubular body preferably comprises four longitudinal slots molded therein. Such longitudinal slots further raise the elasticity of the tubular body for easy expansion thereof upon forcible passage of the abutment means of the ferrule holder therethrough. They also serve as guide means to assure angular positioning of the fibre optic male contact in an insert or connector for the purpose of eccentricity reduction in angled physical contact of the fibre optic core. Preferably, two of said slots are respectively aligned with said windows to further raise the elasticity of the tubular body at that level.
As an alternative, said shoulder means may be formed by an inner annular wall of the tubular body. Within this frame, said abutment means may be formed by a disc shaped portion of the ferrule holder.
Preferably, the ferrule holder is made of two parts screwed into one another, one bearing the abutment means and the other the ferrule.
These and other objects, features and advantages of the invention will become readily apparent from the following detailed description with reference to the accompanying drawings which show, diagrammatically and by way of example only, preferred but still illustrative embodiments of the invention.